This invention relates to auxiliary operator mechanisms utilized on removable control units of a motor control center of the type disclosed in U.S. Pat. No. 4,760,220 issued July 26, 1988 to Ronald J. Fritsch and Francis A. Lubinski, and assigned to the assignee of this application, which patent is hereby incorporated herein by reference. More particularly, this invention relates to an improved drive connection between a handle assembly and a unit interlock slide bar of the auxiliary operator mechanism.
Motor control centers comprise a cabinet having a plurality of vertically arranged compartments which open to a front face of the cabinet. Removable control units are individually contained within respective compartments to be slidably withdrawn through the front opening. Each removable control unit comprises a frame to which motor control apparatus such as contactors, overload relays, fuse blocks, disconnect switches, molded case circuit breakers or motor circuit protectors or combinations of the foregoing are mounted. An operator mechanism is also mounted to the removable control unit for operating the circuit interrupting apparatus of the control unit such as the disconnect switch, molded case circuit breaker or the motor circuit protector. The molded case circuit breaker and the motor circuit protector each have self contained handles and operator mechanisms. Therefore, the operator mechanism of the motor control unit functions as an auxiliary operator for these devices.
The auxiliary operator also functions to operate a unit interlock member which extends to a position of interference with stationary framework of the cabinet in an ON condition of the circuit interrupting apparatus to prevent withdrawal of the removable control unit while the apparatus is electrically live. In an OFF position of the circuit interrupting apparatus and of the auxiliary operator, the unit interlock member assumes a withdrawn position out of interference with the cabinet framework.
The self contained operator handle of molded case circuit breakers or motor circuit protectors assumes one of four positions, i.e. ON, OFF, TRIP and RESET. Through linkage that interconnects the auxiliary operator handle with the circuit interrupting apparatus operator handle, the handle of the auxiliary operator also assumes one of four positions corresponding to the aforementioned ON, OFF, TRIP and RESET positions of the circuit interrupting apparatus handle. In prior art auxiliary operator assemblies, e.g. that of the above referenced patent, the interlock member is a slide bar which is spring biased to an extended position and is driven to a withdrawn position by the auxiliary operator handle when moving to the OFF position, compressing the spring that provides the aforementioned bias to the slide bar. While it is desirable to have the interlock slide bar biased to its extended position unless specifically withdrawn by operating the apparatus to an OFF condition, it has been found that the spring can introduce certain problems with regard to position of either handle. For example, when the auxiliary operator handle is moved to the OFF position and therefore moves the circuit interrupting apparatus handle to the OFF position, the auxiliary operator handle drives the interlock slide bar to a withdrawn position which compresses the interlock slide bar bias spring. Due to tolerances in the auxiliary operator, circuit interrupting apparatus handle/operator and in the interconnecting linkage, the bias provided by the spring of the interlock slide bar may move the auxiliary operator handle upward from a true OFF position sufficiently to permit the interlock slide to bar extend to an interference position, blocking withdrawal of the removable control unit from the motor control center cabinet, necessitating the workman to hold the handle down while attempting to withdraw the control unit. Moreover, when resetting the circuit interrupting apparatus, the handle is moved beyond the OFF position to a RESET position. In so doing, the auxiliary operator handle compresses the interlock slide bar spring further, potentially to a solid condition under adverse tolerance conditions. If compressed solid, the interlock slide bar spring can prevent the auxiliary operator handle from moving fully to the RESET position and therefore prevent resetting of the circuit interrupting apparatus. Although prior art operator mechanisms have adjustment features built in, the effective adjustment range is often quite small and adjustment becomes difficult.